Devices which record data upon optical disks (hereinafter simply termed “disks”) are widespread nowadays. When data is recorded at high speed upon an optical disk whose center of gravity is displaced from its rotational center (hereinafter termed an “out of balance disk”), serious vibration occurs. Thus, with a disk recording device according to the prior art, for example with a DVD recording device, before performing recording upon a disk, a decision is made in advance as to whether or not this disk is an out of balance disk.
As one method for deciding whether or not a disk is out of balance, the method of providing a vibration sensor has been considered. Furthermore, a method of making this decision from the tracking error signal (hereinafter termed the “TE signal”) which is used for performing detection for keeping the pickup upon a predetermined track of the disk, or from the focus error signal (hereinafter termed the “FE signal”), has been proposed (refer to Japanese Laid-Open Patent Publication 2000-182317, Japanese Laid-Open Patent Publication 2004-95079, Japanese Laid-Open Patent Publication 2005-310328, and so on). With this type of method of detecting the TE signal or the FE signal, a structure which is primarily required for keeping the pickup upon the predetermined track may be used. Accordingly, it is not necessary to provide any additional structure such as, for example, a vibration sensor, in order to detect whether or not a disk is out of balance. With prior art methods such as those disclosed in these patent documents of using the TE signal or the FE signal to decide whether or not a disk is out of balance, individual threshold values have been set separately for the TE signal and for the FE signal, and these threshold values have been used for making the decision as to whether or not the disk is out of balance.
In Japanese Laid-Open Patent Publication 2000-182317, there is disclosed a disk device which is endowed with an auto balancer function for corresponding to disk deflection. In this patent document the concept is described of, in order to decide whether or not to deploy the auto balancer function, detecting the TE signal and the FE signal, and comparing them separately with their individual threshold values. The auto balancer function does not manifest any advantageous effect below a certain stipulated rotational speed. On the other hand, when the disk is temporarily rotated at a high speed above the stipulated rotational speed, its advantageous effect is sustained even below the stipulated rotational speed. Accordingly, in this patent document, the concept is described of first detecting the TE signal and the FE signal during a process of raising the rotational speed to a high level, and subsequently detecting the TE signal and the FE signal while lowering the rotational speed to an intermediate level, thus sustaining the advantageous effect of the auto balancer.
In Japanese Laid-Open Patent Publication 2004-95079, the concept is described of deciding whether or not a disk is out of balance by using whether or not the slope of (the TE signal which is detected at some rotational speed (corresponding to the runout amount of the TE signal in the present application)) with respect to (disk rotational speed) is less than some threshold value.
And, in Japanese Laid-Open Patent Publication 2005-310328, there is disclosed an optical disk device which is equipped with a means for making a decision by comparing together the amplitude of TE (corresponding to the runout amount of the TE signal in the present application) in the state when tracking is ON and the amplitude of TE in the state when tracking is OFF, and for changing the recording speed based thereupon, and with a means for making a decision by comparing together the amplitude of the FE signal in the state when tracking is ON and the letter-S shaped amplitude of the FE signal obtained during starting, and for changing the recording speed based thereupon.
However, with methods such as those implemented in the above described prior art devices for deciding whether or not a disk is out of balance by using the TE signal and the FE signal, there has been the problem that the threshold values for the TE signal and the FE signal have each been set individually, so that it has been difficult to define a boundary line with the threshold values for deciding whether or not the disk is out of balance. In other words, since there is some directionality variation in the oscillation of the disk, if one only (or one at a time) of the runout amount of the TE signal, which indicates the amplitude of the error in the horizontal direction with respect to the track position, and the runout amount of the FE signal, which indicates the amplitude of the error in the vertical direction with respect to the track position, is compared with its threshold value, the relationship between these runout amounts and the amount by which the disk is out of balance (in concrete terms, the stability of the servos or the number of errors which are detected when recording or reading data) is not necessarily linear, so that there has been a problem of difficulty in definition of the boundary line in terms of the threshold values.
The present invention has been conceived of in order to solve this type of problem, and it takes as its object to provide an optical disk device which can accurately detect, using the TE signal and the FE signal, whether or not a disk is out of balance.